clouds," said Dr. Bird after an interval of
silence. "We are crossing the Chesapeake now, and things may start to
happen at any moment."

"They're all on their toes, Doctor," replied General Merton. "I
understood in a general way from the President that we are gathering
some important meteorological data for you, but I am ignorant of just
what this data is. Is it a secret?"

Dr. Bird hesitated.

"Yes," he said slowly, "it is. However, I can see no reason why this
secret should not be entrusted to you. We are seeking a means of
ending the great drought which has ravaged the United States for the
past two years."

* * * * *

Before General Merton had time to make a reply, his executive officer
hastened forward from the radio set which was in constant
communication with the units of the fleet.

"Two of the planes on the north end of the line are reporting engine
trouble, sir," he said.

Dr. Bird dropped his glasses and sat bolt upright.

"What kind of engine trouble?" he demanded sharply.

"Their motors are slowing down for no explainable reason. I can't
understand it."

"Are their motors made with sheet steel cylinders or with duralumin
engine blocks?"

"Sheet steel."

"The devil! I hadn't foreseen this, although it was bound to happen if
my theory was right. Tell them to climb! Climb all they know! Don't
let them shut off their motors for any reason, unless they are about
to crash. Turn this ship to the north and have the pilot climb--fast!"

A nod from General Merton confirmed the doctor's orders. The line of
planes kept on to the west, but the flagplane turned to the north and
climbed at a sharp angle, her three motors roaring at full speed. With
the aid of binoculars, the two ships in trouble could be picked out,
falling gradually behind the line. They were flying so slowly that it
seemed inevitable that they would lose flying speed and crash to the
ground.

"More speed!" cried the doctor. "We've elevation enough!"

The altimeter stood at eight thousand feet when the pilot leveled out
the flagplane and tore at full speed toward the laboring ships. The
main fleet was twenty miles to the west.

* * * * *

They were almost above the point where the two planes had first began
to slow down. As they winged along, the three motors of the flagplane
took on a different note. It was a laboring note, pitched on a lower
scale. Gradually the air-